PULLULAN production by Aureobasidium pullulans ATCC 42023 ..... was studied in bioreactor as a high cell density inoculation (HCDI) in two-stage batch culture. Pullulan formation was examined at different agitation rates (100 – 900 rpm) in non-aerated and aerated medium (1.0 vvm) at a range of controlled pH values. Using modified Reeslev & Jensen medium with 5.5 pH, aeration rate of 1.0 vvm and agitation rate of 700 rpm increased pullulan concentration and productivity by 1.73 fold, compared with uncontrolled pH. Under these conditions, maximum pullulan concentration (73.6 gl-1) was obtained after 5 days of fermentation at 28°C. Pullulan yield coefficient relative to biomass, consumed sugar and conversion coefficient after 5 days fermentation period were also increased by about 1.4, 1.07 and 1.14 fold, respectively, comparing with results obtained from aerated medium without controlling initial pH (7.0) at 700 rpm after 4 days of incubation.